src/audio/SDL_sysaudio.h

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "../SDL_internal.h"

#ifndef _SDL_sysaudio_h
#define _SDL_sysaudio_h

#include "SDL_mutex.h"
#include "SDL_thread.h"

/* The SDL audio driver */
typedef struct SDL_AudioDevice SDL_AudioDevice;
#define _THIS   SDL_AudioDevice *_this

/* Audio targets should call this as devices are added to the system (such as
   a USB headset being plugged in), and should also be called for
   for every device found during DetectDevices(). */
extern void SDL_AddAudioDevice(const int iscapture, const char *name, void *handle);

/* Audio targets should call this as devices are removed, so SDL can update
   its list of available devices. */
extern void SDL_RemoveAudioDevice(const int iscapture, void *handle);

/* Audio targets should call this if an opened audio device is lost while
   being used. This can happen due to i/o errors, or a device being unplugged,
   etc. If the device is totally gone, please also call SDL_RemoveAudioDevice()
   as appropriate so SDL's list of devices is accurate. */
extern void SDL_OpenedAudioDeviceDisconnected(SDL_AudioDevice *device);


/* This is the size of a packet when using SDL_QueueAudio(). We allocate
   these as necessary and pool them, under the assumption that we'll
   eventually end up with a handful that keep recycling, meeting whatever
   the app needs. We keep packing data tightly as more arrives to avoid
   wasting space, and if we get a giant block of data, we'll split them
   into multiple packets behind the scenes. My expectation is that most
   apps will have 2-3 of these in the pool. 8k should cover most needs, but
   if this is crippling for some embedded system, we can #ifdef this.
   The system preallocates enough packets for 2 callbacks' worth of data. */
#define SDL_AUDIOBUFFERQUEUE_PACKETLEN (8 * 1024)

/* Used by apps that queue audio instead of using the callback. */
typedef struct SDL_AudioBufferQueue
{
    Uint8 data[SDL_AUDIOBUFFERQUEUE_PACKETLEN];  /* packet data. */
    Uint32 datalen;  /* bytes currently in use in this packet. */
    Uint32 startpos;  /* bytes currently consumed in this packet. */
    struct SDL_AudioBufferQueue *next;  /* next item in linked list. */
} SDL_AudioBufferQueue;

typedef struct SDL_AudioDriverImpl
{
    void (*DetectDevices) (void);
    int (*OpenDevice) (_THIS, void *handle, const char *devname, int iscapture);
    void (*ThreadInit) (_THIS); /* Called by audio thread at start */
    void (*WaitDevice) (_THIS);
    void (*PlayDevice) (_THIS);
    int (*GetPendingBytes) (_THIS);
    Uint8 *(*GetDeviceBuf) (_THIS);
    void (*WaitDone) (_THIS);
    void (*CloseDevice) (_THIS);
    void (*LockDevice) (_THIS);
    void (*UnlockDevice) (_THIS);
    void (*FreeDeviceHandle) (void *handle);  /**< SDL is done with handle from SDL_AddAudioDevice() */
    void (*Deinitialize) (void);

    /* !!! FIXME: add pause(), so we can optimize instead of mixing silence. */

    /* Some flags to push duplicate code into the core and reduce #ifdefs. */
    /* !!! FIXME: these should be SDL_bool */
    int ProvidesOwnCallbackThread;
    int SkipMixerLock;  /* !!! FIXME: do we need this anymore? */
    int HasCaptureSupport;
    int OnlyHasDefaultOutputDevice;
    int OnlyHasDefaultInputDevice;
    int AllowsArbitraryDeviceNames;
} SDL_AudioDriverImpl;


typedef struct SDL_AudioDeviceItem
{
    void *handle;
    struct SDL_AudioDeviceItem *next;
    #if (defined(__GNUC__) && (__GNUC__ <= 2))
    char name[1];  /* actually variable length. */
    #else
    char name[];
    #endif
} SDL_AudioDeviceItem;


typedef struct SDL_AudioDriver
{
    /* * * */
    /* The name of this audio driver */
    const char *name;

    /* * * */
    /* The description of this audio driver */
    const char *desc;

    SDL_AudioDriverImpl impl;

    /* A mutex for device detection */
    SDL_mutex *detectionLock;
    SDL_bool captureDevicesRemoved;
    SDL_bool outputDevicesRemoved;
    int outputDeviceCount;
    int inputDeviceCount;
    SDL_AudioDeviceItem *outputDevices;
    SDL_AudioDeviceItem *inputDevices;
} SDL_AudioDriver;


/* Streamer */
typedef struct
{
    Uint8 *buffer;
    int max_len;                /* the maximum length in bytes */
    int read_pos, write_pos;    /* the position of the write and read heads in bytes */
} SDL_AudioStreamer;


/* Define the SDL audio driver structure */
struct SDL_AudioDevice
{
    /* * * */
    /* Data common to all devices */
    SDL_AudioDeviceID id;

    /* The current audio specification (shared with audio thread) */
    SDL_AudioSpec spec;

    /* An audio conversion block for audio format emulation */
    SDL_AudioCVT convert;

    /* The streamer, if sample rate conversion necessitates it */
    int use_streamer;
    SDL_AudioStreamer streamer;

    /* Current state flags */
    SDL_atomic_t shutdown; /* true if we are signaling the play thread to end. */
    SDL_atomic_t enabled;  /* true if device is functioning and connected. */
    SDL_atomic_t paused;
    SDL_bool opened;
    SDL_bool iscapture;

    /* Fake audio buffer for when the audio hardware is busy */
    Uint8 *fake_stream;

    /* A mutex for locking the mixing buffers */
    SDL_mutex *mixer_lock;

    /* A thread to feed the audio device */
    SDL_Thread *thread;
    SDL_threadID threadid;

    /* Queued buffers (if app not using callback). */
    SDL_AudioBufferQueue *buffer_queue_head; /* device fed from here. */
    SDL_AudioBufferQueue *buffer_queue_tail; /* queue fills to here. */
    SDL_AudioBufferQueue *buffer_queue_pool; /* these are unused packets. */
    Uint32 queued_bytes;  /* number of bytes of audio data in the queue. */

    /* * * */
    /* Data private to this driver */
    struct SDL_PrivateAudioData *hidden;
};
#undef _THIS

typedef struct AudioBootStrap
{
    const char *name;
    const char *desc;
    int (*init) (SDL_AudioDriverImpl * impl);
    int demand_only;  /* 1==request explicitly, or it won't be available. */
} AudioBootStrap;

#endif /* _SDL_sysaudio_h */

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